The development of microwave cooking has had an enormous impact on commercial, industrial and home food preparation. The high speed with which cooking occurs and the broad array of materials suitable for use in microwave ovens have engendered a large number of new uses for microwave ovens. One such use is the popping of kernels of corn. Due to the violent movement of popcorn during the popping process and to the expanded volume of space occupied by the popped corn, an enclosed container for the corn kernels and cooking oil, if used, is indispensible. However, use of this kind of container requires difficult choices among sometimes conflicting performance goals.
One such choice is presented by the alternative materials available to construct the container. A container formed of rigid material, such as microwave transmissive plastic as illustrated in U.S. Pat. No. 4,156,806 to Teich et al, has the advantage of being suitable for reuse but is totally unsatisfactory as a popcorn shipping and dispensing container due to its susceptibility to breakage, its substantial volume and its relatively high cost of manufacture. A container constructed from a disposable material such as paper overcomes many of the disadvantages of rigid reusable containers, but raises questions concerning efficiency and adequate heat dispersal. An early attempt to produce a satisfactory paperboard container is illustrated in U.S. Pat. No. 3,973,045 to Brandberg et al. The container of this patent is a compact gussetted bag made from two plys of paper and has a flexible body which expands to accommodate the increased volume of popped popcorn. While the Brandberg container functions desirably for its intended purpose, it still leaves up to 25 percent of the corn kernels unpopped and 5 percent burned after exposure for approximately two and one half minutes to microwave energy. Other types of expandable paperboard cartons suitable for popping popcorn in a microwave oven are disclosed in U.S. Pat. Nos. 4,279,933 to Astin et al and 4,260,101 to Webinger.
A variety of patents disclose other efforts to remedy the various deficiencies of known containers for the popping of kernels of corn in a microwave oven. For example, a number of solutions involving more efficient use of heat have been proposed to reduce the percentage of corn kernels left unpopped. Some improvement was derived by increasing the heat applied to unpopped corn kernels through use of a dual compartment container, as disclosed in the patent to Brandberg et al (U.S. Pat. No. 4,038,425). The container of this patent has a large upper compartment with inclined walls slanting towards a second lower compartment containing hot melted fat. Unpopped corn kernels are caused to fall back under the force of gravity into the heated lower compartment by sliding or rolling down the walls of the upper compartment.
The patents to Teich et al (U.S. Pat. No. 4,156,806, discussed above,) and to Ishino et al (U.S. Pat. No. 4,335,291) disclose a different approach to improving the efficiency of a popcorn container. In particular, the containers disclosed in these patents rely primarily on concentrating microwave energy at the base of a conically shaped bowl where corn kernels are clumped for the alleged purpose of improving the efficiency and speed of popping. One embodiment disclosed in the Teich et al patent uses a microwave lossy powdered or particulate material in the base area. The lossy material itself heats up and radiates that heat to the kernels located close to it, thereby adding to the heat induced in the corn kernels by direct impingement of the microwaves on the kernels. However, clumping corn kernels in one area of a popping container causes some of the kernels to rest substantially away from the heat generated by the lossy material and, thus, to pop more slowly and less efficiently since they receive a minimal amount of additional heat from the microwave lossy material in the popping container.
As disclosed in the patents to Winters et al (U.S. Pat. No. 4,283,427), Brastad et al (U.S. Pat. No. 4,230,924), Turpin et al (U.S. Pat. No. 4,190,757), Tanizaki (U.S. Pat. No. 3,783,220), Fichtner (U.S. Pat. No. 3,302,632) and Copson et al (U.S. Pat. No. 2,830,162), the use of microwave lossy material is a widely known concept in microwave food preparation containers. However, none of these patents disclose how to employ such lossy material to improve microwave popping of popcorn.
In yet another approach designed to achieve improved microwave popping of popcorn, the patent to Borek (U.S. Pat. No. 4,219,573) discloses a container which is designed to increase the heat available for popping by preventing heat loss in the package through inclusion of a pad designed for heat retention. Again, marginal improvement was noted, but, since the pad is not designed to be interactive with microwaves, it does not itself supply additional heat for application to the corn kernels within the package.
All of the above patents, although making significant contributions to the field of shipping and dispensing kernels for popping in a microwave oven, still leave an undesirably large number of kernels of corn either unpopped or burned. Thus, it has remained an elusive goal in the microwave popcorn popping container art to produce an inexpensive container which strikes a proper functional balance between low cost and efficacy.